LASIK (Laser Assisted In-Situ Keratomileusis) is a procedure commonly used to treat Myopia (nearsightedness), Hyperopia (farsightedness), and Astigmatism through the use of the Excimer Laser. LASIK is an operation which is performed in the Excimer Laser suite. The whole procedure is done under topical anesthesia (numbing drops) and its entire duration is seldom longer than 10 minutes. A suction ring of about 20 mm diameter is placed over the sclera (the white part of the eye) to hold the eye firmly. In performing LASIK, the surgeon first uses a microkeratome, presently with a special oscillating steel blade, to make a partial cut through the front surface of the cornea. This creates a flap of clear tissue on the front central part of the eye. So the automated microkeratome passes across the cornea to create a thin flap. This part of the operation usually takes only a few seconds. The suction ring is then retired from the eye, and the flap is lifted back to leave enough room for the usage of the Laser. The Excimer Laser, which has been previously programmed specifically for the correction of the desired amount of the visual effect, is then applied. A rapid, continuous emission of Laser pulses removes very small precise amounts of corneal tissue. Depending on the type of refractive error, this part of the surgery takes between 30 to 60 seconds. The cornea is then irrigated with saline solution, and the flap is folded back to its original position. Within minutes, the flap adheres itself to rest of the cornea and the LASIK procedure is done. In a couple of days, the cornea will be crystal clear and almost an imperceptible scar will barely be seen.
U.S. Pat. No. 5,133,726 describes a microkeratome. It comprises a holder with a suction ring for attachment to the sclera of a patient's eye. A suction source is connected to the suction ring. A slide is displaceably mounted on the holder in a linear guide. The slide has a plane frontal surface including a transparent plate for contacting the cornea of the patient's eye and slideable over the cornea in a direction parallel to the frontal surface. Attached to the slide is a flexible shaft which is driven by the motor. The end of the shaft has a threaded area which engages a pinion. The pinion drives via transmission gears a drive gear that engages in a rack on the holder to move the slide. At the extreme end of the shaft an eccentric is formed which engages a slot in a sled displaceably mounted on the slide. On the sled a steel cutting blade is mounted with a cutting edge which is parallel to the frontal surface. In operation, when the motor is started it simultaneously oscillates the blade parallel to the cutting edge and moves the slide on the holder. With this microkeratome the surgeon needs a lot of practice to position and to fix the abutting surface provided to stop the motor at the right time, i.e. at the right place. The abutting surface is to guarantee that the desired width of the remaining hinge linking the cut flap of tissue with the remaining cornea is obtained. The speed and oscillation frequency are fixed and have a fixed ratio determined by the gearing.